$ { {1} \times \left[\begin{array}{rr}{-2} & {1} \\ {4} & {-1}\end{array}\right] = {?} } $
Answer: To multiply a matrix by a number, multiply each item of the matrix by the number. ${\left[\begin{array}{rr}{1}\times{-2} & {1}\times{1} \\ {1}\times{4} & {1}\times{-1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{-2} & {1} \\ {4} & {-1}\end{array}\right]}$